#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main() {
    char str[101];
    int seen[256] = {0}; 
    char result[101];
    inti,k = 0;

    if (!fgets(str, sizeof(str), stdin)) {
        printf("Invalid input");
        return 0;
    }

    str[strcspn(str, "\n")] = '\0';

    for (int i = 0; str[i] != '\0'; i++) {
        if (!(isalnum(str[i]) || str[i] == ' ')) {
            printf("Invalid input");
            return 0;
        }
    }

    for (int i = 0; str[i] != '\0'; i++) {
        if (!seen[(unsigned char)str[i]]) {
            seen[(unsigned char)str[i]] = 1;
            result[k++] = str[i];
        }
    }
    result[k] = '\0';

    printf("%s", result);
    return 0;
}